The present invention relates to a semiconductor device and method of manufacturing the same, and more particularly to an integrated circuit device having a bipolar transistor and a method of manufacturing thereof.
Heretofore, a bipolar transistor element has been formed adjacent to a thick field insulating layer which is partially buried in a semiconductor substrate. In the bipolar transistor element, both the base and emitter regions are terminated at the buried portion of the thick field insulating layer. In this case, the PN junction between the base region and the collector region has a sharp curvature in the vicinity of the field insulating layer. Therefore, the breakdown voltage (BV.sub.CBO) between the base region and the collector region becomes a low value because of the sharp curvature of the PN junction. Further, when the field insulating layer is deeply buried into the substrate, silicon crystals near the buried insulating layer include many defects, and therefore, impurities for forming impurity regions are unsuitably deeply diffused along the field insulating layer. The effect by the lattice defects of the silicon substrate has more influence to phosphorus atoms for forming the emitter region rather than to boron atoms for forming the base region. Consequently, the base width along the thick field insulating layer becomes narrower than that of the designed value, then a high breakdown voltage (BV.sub.CEO) between the emitter region and the collector region cannot the expected.